c-thiel commented on code in PR #2880:
URL: https://github.com/apache/iceberg-rust/pull/2880#discussion_r4446292321
##########
crates/iceberg/src/arrow/reader/projection.rs:
##########
@@ -237,6 +269,184 @@ impl ArrowReader {
}
}
+ /// Walks an Arrow `Fields` tree, recording `leaf_idx → variant_field_id`
for every
+ /// leaf that sits inside a variant column (top-level or nested in a
struct/list/map).
+ ///
+ /// The leaf numbering must match [`arrow_schema::Fields::filter_leaves`],
since the
+ /// resulting map is consulted by index in the `filter_leaves` passes
above. In
+ /// particular it mirrors `filter_leaves`' handling of
`Dictionary`/`RunEndEncoded`
+ /// (unwrapped to their value type) and `Union` (each member counted) —
otherwise a
+ /// mismatch would silently shift every variant leaf after it onto the
wrong column.
+ fn collect_variant_leaves(
+ fields: &Fields,
+ leaf_idx: &mut usize,
+ variant_parent: Option<i32>,
+ iceberg_schema: &Schema,
+ leaf_field_id_set: &HashSet<i32>,
+ out: &mut HashMap<usize, i32>,
+ ) -> Result<()> {
+ for field in fields {
+ Self::collect_variant_leaves_in_field(
+ field,
+ leaf_idx,
+ variant_parent,
+ iceberg_schema,
+ leaf_field_id_set,
+ out,
+ )?;
+ }
+ Ok(())
+ }
+
+ fn collect_variant_leaves_in_field(
+ field: &FieldRef,
+ leaf_idx: &mut usize,
+ variant_parent: Option<i32>,
+ iceberg_schema: &Schema,
+ leaf_field_id_set: &HashSet<i32>,
+ out: &mut HashMap<usize, i32>,
+ ) -> Result<()> {
Review Comment:
Done in c2835f9c3, thanks! I went one step further and named it
`leaf_idx_to_variant_field_id`, since it only holds leaves of projected
variants.
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